1. Field of the Invention
This invention relates to a label sheet comprising a substrate carrying an adhesive layer on a surface thereof and, more particularly, it relates to a label sheet comprising a substrate carrying an adhesive layer on a surface thereof and printed information on the other surface that serves as a separable side of the label sheet, wherein said adhesive layer is formed only on a limited area of the surface and/or a parting layer is formed by application on the other surface in order to improve the separability of the label sheet, the efficiency of forming perforations in the label sheet and the adaptability to marking by hand of the separable side of the label sheet.
2. Background Art
A variety of label sheets are known to date and some of the popular applications of label sheets include post cards, envelopes, paper slips, parcels and packaged goods in the fields of mail, delivery, distribution and retailing to list a few. A typical label sheet comprises a substrate carrying printed information in a given area of a surface thereof, which information may be in the form of bar codes and represent the contents of a parcel or package, if the label sheet is to be applied to the parcel or package, and a layer of a pressure-responsive adhesive agent on the other surface. Such a label sheet may additionally comprise an adhesive-repellent cover sheet typically treated with silicon so that the adhesive layer of the label sheet is covered and protected by the cover sheet and the label sheet can be brought to actual use by stripping off the cover sheet from the label sheet with ease or, alternatively, the printed information carrying surface of such a label sheet may be directly treated with silicon to make it adhesive-repellent and operate as a cover sheet for the adhesive layer of another label sheet so that no separate and independent cover sheet may additionally be required. In either case, the label sheet may be part of a larger label sheet and can be separated from the remaining part by ripping it off along perforations and stripping off the cover sheet or simply removing the label sheet from an underlying sheet before it is applied to an object.
A known label sheet of the above described type will be described in greater detail by referring to FIG. 19 of the accompanying drawing n that shows a cross sectional view of a conventional label sheet. In FIG. 19, a rectangular label sheet 91 comprises a substrate 92, an ink layer 95 formed on a surface of the substrate 92 and carrying printed information therein, a separable cover layer 93 of an adhesive-repellent material formed on the ink layer 95 to cover and protect the printed information and an adhesive layer 94 formed on the other surface of the substrate 92. A number of such label sheets are arranged vertically on a one on the other basis to form a multi-layer structure in such a way that the separable cover layer 93 of a label sheet held in contact with the adhesive layer 94 of another label sheet placed directly on it and so on. Such a multi-layer structure of label sheets may be part of a larger rolled or flat label sheet product or a larger comprising a number of such multi-layer structures that are separable from each other along perforations. Thus, an individual label sheet can be separated from the remaining part by ripping it off along perforations and stripping off the cover sheet before is applied to an object.
A conventional label sheet as described above is, however, accompanied by a number of disadvantages. Firstly, since it carries an adhesive on the entire surface of the substrate, it may require s considerable effort for stripping it off from the underlying label sheet, although no particular measures have hitherto been taken to solve this problem. Thus, an attempt to strip off a single label sheet from the remaining label sheets can often end up with unintentionally taking up a number of label sheets at a time. Secondly, in the process of producing perforations in a larger label sheet for defining the boundaries of individual label sheets by means of a perforator, the adhesive can stick to the perforator to reduce the level of precision with which the perforating operation is carried out and give rise to unevenly distributed perforations, which by turn make the label sheets not easily separable and can result in deformed or damaged labels. Additionally, the larger label sheet and the perforator to which the adhesive is sticking may catch and bite each other as the former is fed in and out to cause a trouble of jamming and consequently a reduced productivity. Still additionally, as the perforator needle cuts through the substrate and comes out of it to form a perforation there, the substrate may rise and project around the perforation mainly because of the existence of the adhesive around the perforation. The net result of such projections will be a deformed roll if the perforated label sheets are taken up to form a roll. Such a deformed roll may be not only disagreeable in appearance but also clumsy in the motion of being fed out if it is fitted to a printer or a label holder. If a number of label sheets are not wound up to form a roll but stored as a stack, the adhesive can flow out from the lateral sides of the stack.
On the other hand, an adhesive-repellent agent is applied to the other surface of the substrate of the label sheet to form an adhesive-repellent layer that covers the characters and/or patterns printed on that surface. In other words, two different agents of the adhesive-repellent and the printing ink have to be used on the adhesive-repellent side of the label sheet, involving two separate processing steps, to make the overall label sheet rather thick and costly and the entire manufacturing operation inefficient and uneconomic.
Adhesive-repellent agents used for conventional label sheets typically contain silicon by between 65 and 95% by weight. With such a high silicon content, the surface of the adhesive-repellent layer in hardly adapted to marking by means of a felt-tipped marker, a pencil or a stamp. In other words, any additional information in the form of characters and/or patterns recorded on the exposed surface of the label sheet at the time when it is applied to an object can easily be wiped out by hand or some other thing that may happen to touch it by chance so that any such attempt will find itself abortive.
Known adhesive-repellent cover sheets used for covering and protecting conventional label sheets have to be thrown out once they are peeled off from the respective label sheets to make waste because they have been treated with silicon and hence not feasibly recycled. In an attempt to dissolve this problem, there have been proposed a multi-layer structure of label sheets, where the adhesive layer sides of two vertically successive label sheets are designed to be put together in such a way that each of the two adhesive layer sides is divided into adhesive areas and adhesive-repellent areas and the adhesive areas of either one of the two adhesive layer sides exactly corresponds to the adhesive-repellent areas of the oppositely disposed adhesive layer side. This arrangement is free from the above identified problems so long as the two label sheets are used at a same time. However, the two label sheets are not necessarily used at a same time and, if either one is used before the other one, the adhesive layer side of the remaining one has to be protected by some means so that it may not unintentionally stick to an object, requiring the user to give particular care to it. While the unused adhesive layer side may conceivably be stored by folding it in such a way that its adhesive areas respectively contact with the corresponding adhesive-repellent areas, such a practice will not be possible without exposing some of the adhesive areas. So there exists a demand for a label sheet of the category under consideration that is not accompanied by the above problems.